Oligo(lactic acid)-grafted starch: A compatibilizer for poly(lactic acid)/thermoplastic starch blend.

The objective of this study was to improve the compatibility between poly(lactic acid) (PLA) and thermoplastic starch (TPS) in PLA/TPS blown films by incorporating oligo(lactic acid)-grafted starch (OLA-g-starch) as a compatibilizer. OLA-g-starch with a degree of substitution of 1.2 and degree of polymerization of 2.0 was synthesized via a ring-opening polymerization of lactide initiated by hydroxyl groups of starch. The PLA/TPS blends containing OLA-g-starch were prepared using a twin-screw extruder with a constant weight proportion of PLA to TPS of 50:50 and various concentrations of OLA-g-starch, i.e., 1, 2, 3, and 5%. The obtained blends were blown into thin films using a blown film extruder. SEM confirmed the droplet/matrix morphology of the PLA/TPS blends both with and without OLA-g-starch. Incorporating OLA-g-starch improved the compatibility between the TPS dispersed phase and PLA matrix, as evidenced by the smaller size and better distribution of the TPS phase. As a result, the blends containing OLA-g-starch exhibited up to 280% greater extensibility as well as enhanced water vapor and oxygen barrier properties, water resistance, melt flowability, and thermal stability. The Tg, Tcc, and Tm of PLA in the blends shifted to higher temperatures when OLA-g-starch was incorporated. The obtained PLA/TPS blown film containing OLA-g-starch has the potential to be used as flexible packaging.